The president has not bowed to the main demand of demonstrators in Kiev's Independence Square - and opposition leader Vitaly Klitschko - that he quit.

Mr Klitschko, who has called for early presidential elections before May 25, repeated reports on Saturday that Mr Yanukovych had fled Kiev.

"He has left the capital," Mr Klitschko told an emergency session of parliament, which was debating an opposition motion calling on Mr Yanukovych to resign.

"Millions of Ukrainians see only one choice - early presidential and parliamentary elections."

His comments came as protesters said they had taken control of the presidential administration building in central Kiev.

"He's not here, none of his officials or anyone linked directly to the administration are here," Ostap Kryvdyk, a protest leader, told a Reuters reporter inside the grounds of the administration building.

Protesters had not used force to enter the compound, he added.

However, the UNIAN news agency cited Anna Herman, a lawmaker close to Mr Yanukovych, as saying the president was in the northeastern city of Kharkiv, where he had been due to visit.

And a senior security source told the Reuters news agency that he was still in Ukraine.

"Everything's okay with him," the source said.

Asked whether the embattled leader was in the capital, the source replied: "I cannot say."

Parliamentary speaker Volodymyr Rybak, meantime, has submitted his resignation due to ill health.

Mr Rybak's decision comes after several other members of Mr Yanuvkovych's ruling Regions Party said they were quitting in protest at the use of police force against protesters.

Kiev protesters demand Yanukovych step down

Meanwhile, a demonstrators' council has voted in favour of the deal to form a government of national unity, but not all those who have been occupying Independence Square for almost three months are happy.

"This is just another piece of paper," said Anton Solovyov, 28, an IT worker protesting in the central square.

"We will not leave the barricades until Yanukovych steps down. That's all people want."

British prime minister David Cameron said the deal signed was a real chance to stop the "downward spiral into the nightmare" otherwise facing the country.

US president Barack Obama has discussed the European Union-brokered agreement with his Russian counterpart, Vladimir Putin.

The State Department says their hour-long phone call was constructive, with both leaders urging all sides to refrain from more violence.

White House spokesman Jay Carney says Washington's focus is now on working with its European partners as well as the government and opposition in Ukraine to ensure the agreement is implemented.

"It is in Russia's interest for the violence to end in Ukraine, as it is in the interest of the United States and our European friends, and of course, most importantly, the Ukrainian people, and we welcome the cessation of violence, and we welcome the agreements that have been reached," he said.

"And the measures that have been passed through the parliament, we're still at an implementation stage, and we monitor this very closely."